The present invention relates to infrared sensitive focal plane sensors, and more particularly, to a system that performs a detector array gain and offset correction that also automatically compensates for changes in the operating temperature of the infrared focal plane sensor.
Most infrared sensors currently use an active means to set and regulate the operating temperature of the focal plane. With sensors operating at or near room temperature, this is typically accomplished by means of a temperature control system consisting of temperature sensing devices, a thermal-electric cooler, and temperature control electronics. The time required to establish the desired operating temperature introduces a significant time delay between sensor turn-on and imaging. In addition, the resulting added power, cost, and complexity of the temperature control system combine to significantly limit the potential market for the use of infrared sensor technology.
Focal plane response and offset non-uniformities appear on the output display of an imaging sensor as fixed pattern noise. The non-uniformities are described as noise because they introduce undesirable information in the displayed image. The non-uniformities are described as a fixed pattern because their characteristics do not change (or change relatively slowly) with time. Current infrared sensor systems typically utilize response and offset error correction techniques to minimize the level of fixed pattern noise. With these systems, the response and offset errors remain relatively constant since the infrared sensitive focal planes are maintained at tightly controlled operating temperatures and biases. In current infrared camera systems, however, the operation of the camera can be delayed while the system waits for temperature stabilization.
Accordingly, it is desirable to provide an uncooled infrared sensor with the capability to perform response and offset correction as a function of the sensor""s operating temperature.
The method and apparatus of the present invention relates to an algorithm, and a logical functional architecture for achieving stable operation of infrared sensitive focal plane sensors without the need for active operating temperature stabilization. From a practical stand point, the present invention is also generally applicable to any system that has an approximately linear response that exhibits unwanted sensitivity to operating temperature changes, and whose performance benefits from response and offset correction. The present invention is directed to a correction method for use with an infrared sensor incorporating a focal plane that provides a video input signal, as well as an electrical measurement of the infrared sensor""s operating temperature. Response and offset correction coefficients are then calculated for each detector element of the focal plane array using a linear temperature interpolation of a set of calibrated response and offset correction coefficients that were previously measured and stored into sensor memory during an initial sensor level calibration. The interpolated response and offset correction coefficients are then applied to the video input signal.